Plain bearing composite material comprising a sputtered bearing coating

ABSTRACT

The invention relates to a plain bearing composite material comprising a steel carrier layer, a carrier layer which is cast, sintered or cladded thereon, the carrier layer being made of bronze or brass, and a bearing coating on the carrier layer or on an intermediate layer, the bearing coating being made of a bearing coating material based on aluminium/tin/copper, to increase load-bearing capacity and resistance to wear of the plain bearing composite material. According to the invention, the composition of the plain bearing materials is AlSn(22-30)Cu(2.3-2.8), optionally, comprising upto 2 wt. % Ni, Si, Mn and impurity related elements up to, respectively, 0.5 wt. %, the total quantity thereof not amounting to more than 1 wt. %, and the hardness of the bearing coating being between 110-150 HV 0.002.

This application is the national stage of PCT/EP2004/003494 filed onApr. 2, 2004 and also claims Paris Convention priority of DE 103 55547.1 filed on Nov. 21, 2003.

The present invention concerns a plain bearing composite materialcomprising a steel back layer, a carrier layer of bronze or brass whichis cast, sintered or cladded thereon, and a sliding layer of a slidinglayer material on the basis of aluminium/tin/copper, which is sputteredonto the carrier layer or an intermediate layer.

Conventional plain bearing composite materials are used, in particular,for producing plain bearing shells in automotive applications, inparticular, for bearing the crankshaft or for connecting rod bearingshells, and comprise a sputtered sliding layer on the basis ofaluminium/tin, i.e. produced through cathode sputtering. The Assigneeproduces and distributes e.g. plain bearing shells for automotiveapplications, comprising a sputtered sliding layer of AlSn20 andAlSn20Cu1. The Assignee has also published a product description“PVD-Beschichtete Hochleistungsgleitlager” (PVD coated high-performanceplain bearings) which describes the basics of bearing shell sputtering.

At the end of the 80-es, one tried to produce plain bearing compositematerials for higher loads on the basis of plain bearing compositematerials designed for lesser loads and having a galvanically separatedsliding layer or a cast or cladded sliding layer on the basis ofaluminium/tin with a hardness of approximately 35 to 45 HV 0.002. Onediscovered that the load capacity and wear resistance could be improvedby using sputtered sliding layers having a hardness of between 70 and 90HV 0.002.

However, one quickly realized that a further increase in the hardness ofthe sputtered sliding layers caused undesired embrittlement of thesliding layer material resulting in rapid failure of a plain bearingproduced from such a plain bearing composite material. For this reason,plain bearing composite materials of this type were used having asputtered sliding layer of a hardness in the range between 80 andmaximally 100 HV 0.002.

EP 0 272 447 A2, filed in 1986, discloses an increase in hardness up tovalues of 113 HV at the bearing top and 45 HV at the ends of the bearingshell in an intermediate state prior to thermal treatment, through useof an oxygen atmosphere, with these values being reduced toapproximately 92 HV 0.002 after thermal treatment. This shows the desireto increase the hardness at that time. Today, however, experts try toobtain a moderate hardness in the range between 70 and 100 HV 0.002 forplain bearing composite materials of this type.

DE 36 29 451 C2 discloses a plain bearing composite material of thistype and mentions an AlSn20Cu1 alloy as a sliding layer and anAlSi4Sn15Pb10 alloy. This document also reflects the obsolete desire fora sliding layer of extreme hardness.

EP 0 265 937 A1 of the present Assignee already realizes that it ispossible to obtain suitable sliding layer compositions having a finalhardness of the sputtered sliding layer material of between 75 and 97.5HV 0.002 in connection with AlSn5Cu, AlSn10Cu, AlSn20Cu, AlSn30Cu,AlSn40Cu, AlSn10Pb10Cu. This document also proposes use of an oxygenatmosphere to increase the portion of oxidic components in the slidinglayer material and hence the hardness compared to values ofapproximately 60 HV 0.002.

The stem-shaped layered structure of sputtered sliding layers disclosedin EP 0 300 993 A1 has proven to be entirely unsuitable in practice,since the stem shape is highly brittle, irrespective of the actualcomposition of the sliding layer material.

WO 96/33352 discloses a plain bearing shell for automotive applications,consisting of a plain bearing composite material having a steel backlayer, a carrier layer of lead bronze and a sliding layer of anAlSn20Cu0.25 alloy which is disposed thereon using electron beam vapordeposition. This document broadly mentions that the sliding layermaterial can comprise 15 to 35 weight % of tin, 0.1 to 3.0 weight % ofcopper, and the rest aluminium. The single embodiment, however,discloses the mentioned AlSn20Cu0.25 composition.

It has turned out that a sliding layer disposed through electron beamvapor deposition has a less suitable metallurgical structure and asmaller loading capacity than a sliding layer disposed through cathodesputtering, i.e. a sputtered sliding layer.

U.S. Pat. No. 5,445,896 discloses a plain bearing composite material ofthis type, which mentions a possible composition of 10 to 80 weight % ofSn, 0.1 to 5 weight % of Cu, 0.05 to 3 weight % of Sb, the rest beingAl, and optionally up to 10 weight % of Pb and Bi and moreoveroptionally up to 5 weight % of Si. All embodiments contain 1 weight % ofcopper and 0.5 weight % of antimony. The hardness values stated in table1 are mainly below 100 HV.

It is the underlying purpose of the present invention to improve a plainbearing composite material of this type for producing plain bearingelements, in particular, plain bearing shells for automotiveapplications in such a manner that the loading capacity and wearresistance are improved to adjust a plain bearing element producedtherefrom to the permanently increasing demands of modern combustionengines.

This object is achieved in accordance with the invention with a plainbearing composite material of the above-mentioned type in that thecomposition of the plain bearing material is AlSn(22-30)Cu(2.3-2.8),optionally with up to 2 weight % of each of Ni, Si, Mn, andimpurity-related components of up to 0.5 weight % each, however, intotal maximally 1 weight %, wherein the hardness of the sliding layer is110 to 150 HV 0.002.

The present invention has surprisingly shown that by increasing thecopper content to the claimed range and with a tin content within theclaimed range, the loading capacity and the wear resistance can beincreased by increasing the hardness of the sliding layer to a range ofbetween 110 and 150 HV 0.002 without causing embrittlement of thesliding layer material. Up to now, it was assumed that it is notpossible to obtain a suitable plain bearing composite material or plainbearing element made therefrom for automotive applications using plainbearing composite materials of this type of more than 100 HV 0.002,since it was assumed that an increase in hardness would reduce theadaptive behavior and the capacity of embedding microscopic foreignmaterials into the plain bearing material to an unacceptable extent. Onealso assumed that the adhesive strength of the sputtered sliding layerwould no longer be sufficient to prevent separation. It has nowsurprisingly turned out that this does not apply for the claimedcomposition of the plain bearing material and that it is possible toobtain a very great hardness resulting in good wear resistance, therebystill unexpectedly providing sufficient ductility for embedding foreignbodies.

There is a test method that is easy to perform for testing, in advance,the suitability of a plain bearing composite material of this type forcommon loads that occur in combustion engines. One can assume that thesliding layer is sufficiently ductile if scratching the sliding layerwith a fine blade, e.g. a carpet knife, down to the carrier layer,produces a material displacement along the scratch without sliding layerparticles being chipped off, which would be the case if the slidinglayer material were excessively brittle.

In contrast to the opinion of the experts that plain bearing compositematerials of this type should have a moderate hardness in the range ofbetween 70 to maximally 100 HV, the present invention showed that thecomposition with greater hardness in the claimed range had sufficientductility of the sliding layer material, to ensure good embeddingbehavior or adjustment behavior of the sliding layer material duringoperation. This is the pre-condition for permanent good wear resistanceand high loading capacity.

Preferred compositions of the sliding layer material and preferredhardnesses of the sliding layer are stated in the dependent claims.

A lead-free sliding layer material or a completely lead-free plainbearing composite material have proven to be particularly advantageous.

In one preferred embodiment of the inventive plain bearing compositematerial, the sliding layer material is composed of anAlSn(22-30)Cu(2.3-2.8) alloy, at most containing impurity-relatedcomponents, preferably less than 0.05 weight % each.

A preferred composition of the inventive plain bearing material isAlSn25Cu2.5.

It has turned out that an Inventive plain bearing composite material ora plain bearing element produced therefrom has a higher wear resistanceand additionally higher loading capacity compared to a compositematerial of AlSn20Cu1 sliding layer material of this type. The slidinglayer or the sliding layer material having a hardness within the claimedrange still has sufficient ductility to achieve good embedding andadaptive behavior, such that, in total, the inventive material can bearhigher loads and has a higher wear resistance compared to conventionalmaterials or sliding elements produced therefrom.

1-12. (canceled)
 13. A plain bearing composite material comprising: asteel back layer; a carrier layer of bronze or brass which is cast,sintered or cladded onto said steel back layer; and a sliding layersputtered onto said carrier layer, said sliding layer comprisingAlSn(22-30)Cu(2.3-2.8), said sliding layer having a hardness between 110and 150 HV 0.002.
 14. The plain bearing composite material of claim 13,further comprising up to 2 weight % of each of Ni, Si, and Mn, andimpurity-related components of up to 0.5 weight % each, but in total notmore than 1 weight %.
 15. The plain bearing composite material of claim13, further comprising an intermediate layer disposed between saidcarrier layer and said sliding layer.
 16. The plain bearing compositematerial of claim 13, wherein said sliding layer is lead-free.
 17. Theplain bearing composite material of claim 16, wherein the plain bearingcomposite material is lead-free.
 18. The plain bearing compositematerial of claim 13, wherein the plain bearing composite materialscontains no antimony.
 19. The plain bearing composite material of claim13, wherein a composition of said sliding layer isAlSn(22-28)Cu(2.3-2.8).
 20. The plain bearing composite material ofclaim 19, wherein a composition of said sliding layer isAlSn(23-28)Cu(2.3-2.8).
 21. The plain bearing composite material ofclaim 20, wherein a composition of said sliding layer isAlSn(23-27)Cu(2.4-2.7).
 22. The plain bearing composite material ofclaim 13, wherein said hardness of said sliding layer is 110 to 140 HV0.002.
 23. The plain bearing composite material of claim 22, whereinsaid hardness of said sliding layer is 110 to 130 HV 0.002.
 24. Theplain bearing composite material of claim 23, wherein said hardness ofsaid sliding layer is 115 to 130 HV 0.002.
 25. The plain bearingcomposite material of claim 13, wherein said carrier layer is formed bya CuPb(8-25)Sn(2-12) alloy.
 26. The plain bearing composite material ofclaim 13, wherein said carrier layer is formed by a CuZn(20-32) alloy.27. The plain bearing element, a plain bearing shell for automotiveapplications, a crankshaft bearing shell, or a connecting rod bearingshell comprising the plain bearing composite material of claim 13.